The present invention relates to wireless communication networks having systems with overlapping coverage areas. More specifically, the present invention relates to inter-system handovers within wireless communication networks.
Referring to FIG. 1, there is shown a Universal Mobile Telecommunications System using Time Division Duplex 10 (hereinafter “TDD system”) overlapping a wider-area Universal Mobile Telecommunications System using Frequency Division Duplex 12 (hereinafter “FDD system”). FIG. 2 shows the opposite scenario, of an FDD system 12 overlapping a wider-area TDD system 10. Handover between the two systems 10, 12 is possible, but requires that measurements be made by wireless transmit and receive units (WTRUs) and that those measurements be forwarded to the radio network controller (RNC), which performs the handover decision.
Event 2b, as defined in “3GPP TS 25.331 V4.8.0 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol Specification (Release 4)”, dated December 2002 (hereinafter, “the Standard”), may be used when performing an inter-system handover (i.e., a handover between a TDD system 10 and a FDD system 12). Event 2b is defined in the Standard as an event where “the estimated quality of the currently used frequency is below a certain threshold and the estimated quality of a non-used frequency is above a certain threshold.” It is important to note that the non-used frequency is always a frequency of the system to which a WTRU will be handed over. Therefore, evaluation of inter-system handovers (i.e., handovers between TDD and FDD systems) using Event 2b requires two thresholds: (1) the minimum quality condition for the TDD system 10 and (2) the minimum quality condition for the FDD system 12.
The minimum quality condition for the TDD system 10 is based on the received signal code power (RSCP) of the primary common control physical channel (PCCPCH; hereinafter collectively referred to as “P-CCPCH RSCP”). The minimum quality condition for the FDD system 12 may be based on either the RSCP of the common pilot channel (CPICH; hereinafter collectively referred to as the “CPICH RSCP”) or the signal-to-noise ratio (Ec/No) of the common pilot channel (CPICH; hereinafter collectively referred to as “CPICH Ec/No”).
These minimum quality values are highly dependent on the particular deployment (e.g., Manhattan microcell deployment), and could possibly be set manually for each cell in a TDD/FDD border area. The interference patterns are different in the different deployments. For example, the standard deviation of lognormal fading has different values for different deployments, which is higher for microcells than for urban areas in general. Also, the multipath interference is different for different deployments. This means that while the quality level of a beacon of −105 dBm is sufficient to support communication in one cell due to low interference, it may not be sufficient to support communication in another cell, because the interference might be higher. In order to permit ease of administration, it is of interest to provide an automated method and system for determining the thresholds needed for evaluating inter-system handovers.